118 



But although the Muschel-kalkstein has not yet been detected, 

 and probably may not exist in any considerable force in Eng- 

 land, it would be premature to assert that its equivalent may 

 not still be detected among our strata ; and this, with other cir- 

 cumstances, renders a good monograph of the new-red-sandstone 

 formation, in the central and southern counties, a desideratum of 

 importance. The general boundaries of the formation have been 

 correctly traced ; but the internal details remain to be investi- 

 gated : and besides the necessity of searching in the upper part of 

 the formation for the equivalent of those beds which are so con- 

 spicuous on the continent, the relations of the porphyritic masses 

 of Devonshire and other places (which, it is remarkable, are found 

 in combination with the saliferous red sandstone, not only in various 

 parts of Europe, but even in India*) are still very obscure. The 

 publications of M. Charbautf, M. Elie de Beaumont^, and Messrs. 

 Oeynhausen, Dechen, and De la Roche § will be found to assist 

 materially in these investigations. 



The Magnesian-limestone itself, according to Mr. Sedgwick, 

 admits of natural subdivision into five portions, which, in a descend- 

 ing order are: — 1. A series of red sandstone and marl, superior to the 

 dolomites, and subdivided into two portions ; the equivalents of the 

 keuper and the hunter -sandstein. — 2. Limestones, containing magne- 

 sia and beds of dolomite, unequally diffused, but in much less pro- 

 portion than in the lower parts of the series. — 3. Red marl and gyp- 

 sum, comparatively of small extent. —4. The great central deposit 

 of yellow limestone, exhibiting various modifications of dolomite, 

 frequently concretional, in some cases oolitic ; all of which appa- 

 rently result from internal change of structure, subsequent to the 

 mechanical deposition of the mass. These last formations (4, 3, and 

 2) represent the Ranchtvacke, Asche, and foliated StinJcstein, the brec- 

 cias, and gypsum of the Thuringerwald. — 5. Variegated marls, with 

 irregular beds of compact limestone, Zechstein. This formation is not 

 co-extensive with the yellow limestone, but its place is constant; and 

 its subordinate marl-slate is particularly distinguished by its Fossils; 

 among which are impressions of ferns, and the remains of fishes, 

 some of them identical with those of the copper-slate of Thuringia. 

 — 6. And lastly, an extensive deposit of coarse siliceous sandstone 

 (rothe-todte-liegende), of very unequal thickness ; the upper beds 

 of which are sometimes unconformable to the limestones which rest 

 upon them. It is satisfactory therefore to find, that the great mass 

 of strata, from the oolites down to the coal, admits precisely of the 

 same subdivisions in the north of England, as upon the continent. 



With respect to the theory of these magnesian formations, Mr. 

 Sedgwick ascribes their production to the mechanical destruction 



* Geological Transactions, Second Series, vol. i. page l6o. 



f " Environs de Lons le Saunier.'' — Annales des Mines, 1819, v. 5/9. 



J " Observations sur quelques Terrains secondares du Systeme des 

 Vosges :" Paris, 1828 ; also published in the Annales des Mines for 1827. 



§ " Geognostische Umrisse den Rheinlander, zwischen Basil and 

 Maintz:" 2 vols. 1825. 



